In order to allow sharing of data stored on a hard disc by plural users, conventional network management systems are generally provided with a database for managing management information such as stored locations of all data on a network and names of files. There occurs a situation where more than one user simultaneously requests access to the data conforming to the data management information. To realize such access requests, there exists a network management system as shown in the block diagram of FIG. 17.
In the prior art system configuration of FIG. 17, N number of units of nodes 1701 to 170N having a functionality of a personal computer, for example, and a database 1704 are connected through an Ethernet network. Also, a hard disc 1705 having data 1706 is connected to the database 1704. Referring to FIG. 17, a description will be given in the following for the case of two or more nodes simultaneously having access to the same data.
In general, when a node (1) 1701 is having read access to the data 1706, access from other nodes to the data 1706 is approved only when it is read access. However, when plural nodes execute simultaneous read access to the data 1706 in this way, the data transfer rate per node becomes lower with increasing number of nodes which have access as the transmission band of the network and the input/output (I/O) band of the hard disc are divided by the number of nodes that have access. This reduction in the bands has not caused any problem when having access to data that does not require real-timeness.
In the prior art network management system described above, when simultaneous access from plural nodes to the same data is executed, there is a risk of data transfer being interrupted as the transmission band of the network for each node and the I/O band of the hard disc are not guaranteed; for instance, when having access to a stream of data such as video data which requires real-timeness, it suffers a problem of not being able to guarantee bands to a node which is having preceding read access.